When does your period come back after pregnancy?

Normally lactating mother do not get periods till 3 months. Still u need to

take precautions preventing next pregnanacy.I have the example as our mother in law casually mentioned that lactating mother do not conceive. By my wife did conceive even with out periods.So am blessed with first son and second son with a gap of 12 months 15 days and second child

was weak and took more time to recoup.